Condition sensor for medical device package

ABSTRACT

A package in which a medical device is stored, the package comprising an outer shell providing a vapor barrier between an interior space inside the outer shell and an exterior environment, a medical device positioned in the interior space inside the outer shell, the medical device including a liquid-containing element that is subject to drying out as liquid from the liquid-containing element vaporizes and travels from the interior space to the external environment, a condition sensor comprising two metallic elements, each of the two metallic elements being composed of different metals, with each of the different metals selected so that the two metallic elements form an anode and a cathode of an electrochemical cell, each of the two metallic elements being in electrical contact with a conductive water-containing element, so that the water-containing element forms the electrolyte of the electrochemical cell, and an electrically conductive path extending from each of the metallic elements to a location wherein the electrochemical potential formed between the metallic elements can be measured to provide an indication of the degree to which the conductive water-containing element has dried out.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority toU.S. application Ser. No. 11/481,245, filed on Jul. 5, 2006, now issuedas U.S. Pat. No. 8,577,462. This application is hereby incorporated byreference.

TECHNICAL FIELD

This invention relates to sealed packages for medical devices.

BACKGROUND

There is a growing trend toward the replacement of multiple usedefibrillator paddles with single-use disposable therapeutic electrodesfor defibrillation, external transthoracic pacing, or the combination ofboth. This trend is driven by numerous factors including, but notlimited to: (1) convenience related to not having to apply a conductivemedia (e.g., gel), (2) speed of care when switching from delivering adefibrillation shock to a pacing current, (3) caregiver safety in thatcontact with the patient can be avoided as the therapy can be deliveredremotely from the host device, and (4) increased use of defibrillatorsincorporating algorithms that analyze the presented ECG rhythm forappropriateness of therapeutic (shock) delivery. These applicationstypically work only with single-use, disposable therapeutic electrodes.

Defibrillation of cardiac arrest is a time sensitive matter. It is welldocumented that for every minute delivery is delayed, the chance ofsurvival falls 7 to 10 percent. One way manufacturers have addressed thetime to shock issue, has been to create electrodes that can bepre-connected to a defibrillator. If electrodes are not pre-connected orpresent, valuable time will be lost, and chance of survival diminishedas responders must address this matter.

Owing to many factors both chemical and environmental in nature,single-use therapeutic electrodes have a finite shelf life.Manufacturers typically label individual electrodes with specific datesof expiration beyond which therapeutic delivery cannot be insured. It isincumbent on the operator to read the electrode labeling prior to use toinsure a non-expired electrode is deployed for therapy.

Electrode packaging is designed to be both airtight and watertight. Thisis to minimize environmental fluctuations that might shorten the usefullife of an electrode. Should an electrode package be breached, chemicalreactions will be accelerated and shelf life shortened.

Checking for the condition of an electrode package, or reading theexpiration date are time consuming are potential points of error thathave the potential to adversely affect a defibrillator's therapeuticcapabilities.

SUMMARY

In a first aspect, the invention features a package in which a medicaldevice is stored, the package comprising an outer shell providing avapor barrier between an interior space inside the outer shell and anexterior environment, a medical device positioned in the interior spaceinside the outer shell, the medical device including a liquid-containingelement that is subject to drying out as liquid from theliquid-containing element vaporizes and travels from the interior spaceto the external environment, a condition sensor comprising two metallicelements, each of the two metallic elements being composed of differentmetals, with each of the different metals selected so that the twometallic elements form an anode and a cathode of an electrochemicalcell, each of the two metallic elements being in electrical contact witha conductive water-containing element, so that the water-containingelement forms the electrolyte of the electrochemical cell, and anelectrically conductive path extending from each of the metallicelements to a location wherein the electrochemical potential formedbetween the metallic elements can be measured to provide an indicationof the degree to which the conductive water-containing element has driedout.

Preferred implementations of this aspect of the invention mayincorporate one or more of the following. The medical device stored inthe package may comprise at least one electrode, and wherein theelectrode may include a metallic layer in electrical contact with aconductive liquid-containing layer through which electrical current maybe delivered to a patient when the electrode has been applied to apatient, the conductive liquid-containing layer may be subject to dryingout as liquid from the liquid-containing layer vaporizes and travelsfrom the interior space to the external environment, and wherein thecondition sensor may provide an indication of whether theliquid-containing layer has dried out sufficiently that the electrodeshould not be used. The metallic elements of the condition sensor may beseparate from the metallic layer in the electrode. The electrode maycomprise a defibrillation electrode. The conductive liquid-containinglayer of the electrode may contain water and may comprise an aqueousgel. The aqueous gel may comprise a solid gel. The aqueous gel maycomprise a liquid gel. The water-containing element of the conditionsensor may comprise an aqueous gel layer. The metallic elements of thecondition sensor may be thin metallic layers and the aqueous gel may bea thin gel layer in contact with each of the metallic layers. The thingel layer may be a different layer from the conductive liquid-containinglayer of the defibrillation electrode. The condition sensor may beconfigured so as to be retained in the package when the defibrillationelectrode has been removed from the package. The electrically conductivepaths extending from each of the metallic elements may compriseelectrical wires extending from the metallic elements at least to theouter shell. The electrochemical potential may be measured inside thepackage and communicated to the exterior of the package. The inventionmay further comprise a gasket element at the perimeter of the outershell, the gasket element may be shaped and positioned so that onesurface of the gasket element may be exposed to the interior spacewithin the outer shell and another surface of the gasket element may beexposed to the exterior environment, the electrically conductive pathsfrom the metallic elements of the condition sensor may extend throughthe gasket element from the interior space to the exterior environment.The gasket element may be configured so that when the package is openedand the defibrillation electrode applied to the patient, the gasketelement may be removed from the package which may cause the electricallyconductive paths connected to the further electrical element to bebroken. The condition sensor may further comprise a resistive elementelectrically connected between the two metallic elements. The resistanceof the resistive element may be variable. The metals used in themetallic elements of the condition sensor may include at least one metalthat is the same as the metal used in the defibrillation electrode.

In a second aspect, the invention features a defibrillator for providinga defibrillation pulse to electrodes applied to the chest of a patient,the defibrillator comprising a pair of electrical outputs for deliveringthe defibrillation pulse to at least one defibrillation electrode, apair of electrical inputs for measuring the electrical potential of anelectrochemical cell formed within a package containing thedefibrillation electrode prior to use of the electrode, processingcircuitry and associated software for comparing the electrical potentialto one or more thresholds to determine whether a gel layer of thedefibrillation electrode remains sufficiently moist for the electrode tofunction.

Preferred implementations of this aspect of the invention mayincorporate one or more of the following. The comparison may determinewhether the electrical potential is below a threshold. The comparisonmay determine whether the rate of change of the electrical potential isabove a threshold. The processing circuitry and associated software mayinclude the capability to call for delivery of a warning indication tothe user based on the outcome of the comparison. At least one thresholdmay be determined by reading a value stored in a memory deviceassociated with the defibrillation electrode.

Among the many advantages of the invention (some of which may beachieved only in some of its various aspects and implementations) arethe following: The condition of a medical device (e.g., a defibrillationelectrode) within a sealed package can be determined automatically,thereby increasing the reliability of the equipment that uses themedical device.

Other features and advantages of the invention will be found in thedetailed description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a defibrillator implementation of theinvention.

FIG. 2 is a perspective view of the defibrillator of FIG. 1 with anelectrode package shown removed.

FIG. 3 is a side elevation view of the defibrillator of FIG. 1 lookingtoward the side with the electrode package.

FIG. 4 is a cross-sectional view taken along section 4-4 in FIG. 3.

FIG. 5 is a plan view of the electrode package after being opened toexpose its contents.

FIG. 6 is a plan view of the two defibrillation electrodes stored insidethe electrode package.

FIG. 7 is an exploded, cross-sectional view taken along 7-7 in FIG. 6.

FIG. 8 is an exploded, cross-sectional view taken along 8-8 in FIG. 6.

FIG. 9 is a plan view of the condition sensor (electrochemical cell)secured inside the electrode package.

FIG. 10 is an exploded, cross-sectional view taken along section 10-10in FIG. 9.

FIG. 11 is a schematic view of the electrical connections between thecontents of the electrode package (electrodes, condition sensor, CPRpuck) and the electrode package connector.

FIG. 12 is a plan view showing the rigid shell of the electrode packagewith its removable lid removed and its contents removed.

FIG. 13 is a partial cross-sectional view taken along section B-B inFIG. 12 showing a cross section through an inner end of the gasketelement of the electrode package.

FIG. 14 is a partial cross-sectional view taken along section A-A inFIG. 12 showing a cross section through an outer end of the gasketelement of the electrode package.

FIG. 15 is a plan view of the gasket element.

FIG. 16 is an end view of the gasket element.

FIG. 17 is a cross-sectional view taken along section 17-17 in FIG. 15.

FIG. 18 is a perspective view of the gasket element.

FIG. 19 is another perspective view of the gasket element.

FIG. 20 is a block diagram of the electronics and components of thedefibrillator of FIG. 1.

FIG. 21 is a plan view showing the triangular electrode of FIGS. 6-7applied to a the chest of a patient.

FIG. 22 is a plan view showing an alternative, crescent shaped electrodethat could be used in place of the triangular electrode.

DETAILED DESCRIPTION

There are a great many possible implementations of the invention, toomany to describe herein. Some possible implementations that arepresently preferred are described below. It cannot be emphasized toostrongly, however, that these are descriptions of implementations of theinvention, and not descriptions of the invention, which is not limitedto the detailed implementations described in this section but isdescribed in broader terms in the claims.

FIGS. 1-4 show an external defibrillator 10 (e.g., a hospital crash cartdefibrillator, such as the R Series manufactured by ZOLL Medical ofChelmsford, Mass.). User interface elements (graphical display, speaker,microphone, input buttons and dials) are provided on the front face ofthe defibrillator. Attached to the right side of the defibrillator is anelectrode package 12, which is removable from the defibrillator, asshown in FIG. 2, and normally electrically connected to thedefibrillator by cable 14 even when the defibrillator is not in use. Themulti-conductor cable 14 emerging from the electrode package passesthrough a connector (not shown in FIGS. 104, but shown in the schematicof FIG. 11) and divides into two cables 11, 13 which attach to the backof the defibrillator. A removable lid 16 is removed (by grasping tab 18)to open the defibrillator package.

The electrode package 12 includes a rigid base (or tray) 20(polypropylene), which with the removable lid 16 (foil lined paper)constitutes the outer shell of the package. The base and lid provide amoisture barrier to prevent the gel layers of the electrodes from dryingout during the shelf life of the package. The lid is heat sealed to theperimeter of the base (tray). The rigid base (a molded polymer part) isremovable snapped into the receptacle 22 on the side of thedefibrillator also used to secure a defibrillator paddle. Upper andlower flexible clips 24, 26 snap into engagement with mating elements ofthe receptacle 22. Engagement of the flexible clips 24, 26 is shown inthe cross section of FIG. 4, which shows the electrode package snappedinto place on the side of the defibrillator.

FIG. 5 shows the electrode package with lid 16 peeled back to expose thecontents of the package. A first defibrillation electrode 28 (generallysquare in this plan view) for the back (posterior) of the patient'schest is adhered to a release liner (not shown) secured to the insideface of lid 16. Electrode 28 is peeled off of the release liner andadhered to the back of the chest.

A second defibrillation electrode 30 (generally triangular in this planview) for the front (anterior) of the patient's chest is adhered toanother release liner (not shown) secured to the rigid based of theelectrode package. Electrode 30 is an assembly of a defibrillationelectrode and three ECG monitoring electrodes, and is described inco-pending U.S. patent application Ser. No. 11/055,572, filed on Feb.11, 2005, hereby incorporated by reference.

A device for assisting CPR, known as a CPR puck or pad 32, is alsostored within the electrode package. A similar CPR pad is described inU.S. Pat. No. 6,782,293, hereby incorporated by reference. It includesan accelerometer for measuring movement of the chest during CPR.

The fourth element within the electrode package is a condition sensor 34that assists the defibrillator in determining whether theliquid-containing (gel) layers of the defibrillation electrodes arestill sufficiently moist to function properly. The condition sensor 34is not intended to be removed from the package, as it is not used duringdefibrillation.

Various electrical conductors pass into the electrode package to connectthe contents with the defibrillator. These conductors pass through agasket element 36 that is sealed between the rigid base 20 and removablelid 16 of the package. When the electrodes and CPR puck are removed fromthe package, the gasket element is also removed, as the electricalconductors for the electrodes and CPR puck extend through the gasketelement.

FIGS. 6-8 show the two defibrillation electrodes 28, 30 in greaterdetail. The triangular front electrode 30 is shown in FIGS. 6-7. Theconstruction of the electrode is shown in exploded, cross-sectional viewin FIG. 7. A conductive liquid-containing layer 40 (solid gel) contactsthe patient's skin, and conveys electrical current from the metalliclayer 42 (tin plate or other metallic material such as silver chloride)to the patient. The gel and tin layer are supported on foam layer 44,which carries adhesive to secure the electrode to the patient. Themetallic layer is connected to wire 46 through which the defibrillationpulse is delivered from the defibrillator. A foam insulator layer 48covers the area where the metallic layer and wire emerge from theelectrode. A label 50 is applied over the foam layer 44.

FIG. 21 shows the triangular electrode in place on the chest of thepatient. The triangular shape greatly facilitates application of theelectrode to the chest in the vicinity of a breast. The front electrodeis adhered at the edge of the patient's breast, and the triangular shapehas an advantage over circular or square electrodes in this location.These other shapes tend to fold or roll back on themselves. E.g., with asquare electrode in this location, one corner of the electrode rides upon the breast, and will tend to roll back off the breast. This alsotends to occur with circular electrodes. But with the triangular shapethe problem is usually avoided. Another shape that will work well is acrescent shape, as shown in FIG. 22, with the smaller radius of thecrescent closest to the breast. It is the lateral perimeter of theelectrode that has the triangular or crescent shape.

Three ECG monitoring electrodes are built into the three corners of theelectrode. Each monitoring electrode includes a solid gel layer 52 forcontacting the patient, a conductive stud 54 (Ag/Cl) in contact with thegel layer, and conveying electrical potentials from the gel layer to thesnap conductor 56 (Ni/Brass) to which a monitoring wire is connected.Alternatively, the snap conductor can be eliminated, and the ECGmonitoring wires connected directly to the conductive studs 54.

The square defibrillation electrode 28 is shown in exploded,cross-sectional view in FIG. 8. It includes most of the same layers asthe other defibrillation electrode (identified in the figure by usingthe same reference numeral for corresponding parts).

FIGS. 9-10 show the condition sensor 32, which functions as anelectrochemical cell producing an electrical potential that is measuredby the defibrillator to determine whether the moisture in the aqueouslayer of the sensor has dried out. As the aqueous layer dries out(because moisture has escaped from the electrode package, e.g., becausethe package has been damaged), the potential of the electrochemical cellwill fall off in magnitude. Once it falls below a threshold, indicatingthat the aqueous layer of the sensor has dried out, the defibrillatorconcludes that there is a high probability that the liquid-containinglayers of the defibrillation electrodes have also dried out, and awarning prompt is delivered and the defibrillator may not deliver adefibrillation pulse to the electrodes.

Various other alternative tests could be applied to decide that theelectrode is no longer suited for its intended use. E.g., the potentialcould be sampled frequently enough to establish a rate of change, andtoo high a rate of change could be a basis for deciding that somethingis wrong with the electrode. Depending on the circuitry used to measurethe potential, a problem with the electrode could be detected by avoltage exceeding a threshold, and there could be multiple limits thatthe measured voltage is tested against.

FIG. 10 shows an exploded, cross-sectional view of the condition sensor.At the top of the stack of layers is a styrene release liner 60, whichis removed when the sensor is installed in the electrode package, toexpose adhesive on the vinyl mask layer 62, which is adhered to aninterior surface of the electrode package to secure the condition sensorwithin the package. A aqueous layer 64 (gel) is positioned below thevinyl mask. A first metallic layer (metallic element) 66 (tin) is incontact with the gel. That is followed by an insulator layer 68 that islarger in area than the tin layer. Following the insulator layer is asecond metallic layer (metallic element) 70 (aluminum) that is also incontact with the gel along its periphery outside of the extent of theinsulator layer 68. A foam backing layer 72 and foam cover 74 completethe sandwich of layers. A wire 76 (electrical conductor) is connected toeach of the metallic layers (both shown in FIG. 9; one shown in FIG.10). A bridging resistor 78 (approximately 100K ohms) is connectedacross the two metallic layers to control the rate of theelectrochemical reaction (the size of this resistor will vary with themetals and gels used in the electrochemical cell and with other factorswell known to those skilled in the art). The wires 76 are connected tothe metallic layers with rings 80 and sockets 82. A foam insulator layer84 and length of tape 86 are positioned between the aqueous layer 64 andthe first metallic layer 66.

FIG. 11 is an electrical schematic of the electrode package 12.Defibrillator electrodes 28, 30, condition sensor 32, and CPR puck 34are shown within the electrode package. Cables connecting these elementstot the defibrillator pass out of the package through gasket element 36(shown diagrammatically as a dashed rectangle in the schematic). Eachdefibrillation electrode has a single electrical conductor 90 configuredto carry a high voltage signal. Three shielded wires 92 connect to thethree ECG monitoring electrodes (designated by the snap conductors 56 atthe locations of the monitoring electrodes. Two wires 94 connect to thecondition sensor 32 (although in a preferred embodiment the electricalconductors connecting to the condition sensor are shared with otherwires (e.g., one or more of the CPR puck wires). Eight wires 96 connectto the CPR puck.

All of wires 90, 92, 94, and 96 pass through the gasket element 36, andextend to an electrode package connector 102 (electrodes end connector),which is plugged into the patient end connector 104 of a cable that runsback to the defibrillator. The two connectors 102, 104 are shown matedin FIG. 11.

An electronic memory device 100 (e.g., a Dallas Maxim semiconductorchip, Part No. DS2431) is built into connector 102. A variety ofinformation is stored on the chip, including: an authentication code, aconfiguration code (e.g., whether the package contains ECG monitoringelectrodes, a CPR puck, or only defibrillation electrodes), the type ofelectrodes (adult or pediatric), the expiration date of the electrodepackage, the serial number, and the date of manufacturing andmanufacturing line. Other information (or less information) could bestored on the chip.

FIGS. 12-19 show the gasket element through which the electricalconductors extend. The gasket element is shown in perspective view inFIGS. 18 and 19. It has gradually tapered extensions 108 extending inthe direction in which it is adhered to the perimeter of the sealbetween the rigid base 20 and removable lid 16 of the package 12. A bead110 of silicone adhesive seals one surface of the gasket element to therigid base 20 of the package. This material is chosen so that the gasketwill part from the rigid base when the electrodes are removed from thebase. Between the tapered extensions 108 is a central portion 112.

The gasket element has at least one surface exposed to the interior ofthe electrode package and at least one surface exposed to the exteriorof the package. Holes pass through the gasket element from a surfaceexposed to the interior to a surface exposed to the exterior. Threeelectrical paths for the monitoring electrodes pass through three holes120. Eight smaller holes 122 (or one narrow opening) provide access forthe electrical paths connecting the CPR puck.

When the gasket releases from the rigid base of the electrode package,certain electrical connections can be broken. For example, a conductiveshorting element 130 that shorts across the two high-voltagedefibrillation wires 90 (to allow testing of the integrity of theseelectrical pathways outside of the electrical package) is broken away. Asecond electrical connection that is broken is the connection to thecondition sensor. Wires 94 (or their equivalent) that provide electricalpathways to the metallic layers of the condition sensor are disconnectedfrom the condition sensor. This is necessary because the conditionsensor in this implementation remains in the electrode package, as itsusefulness as a package condition sensor has ended with the opening ofthe package.

Various techniques could be used to accomplish the disconnection ofthese electrical connections when the gasket element is removed. In theimplementation shown herein, conductive posts 150, extending upward fromthe rigid base of the package, and normally received in conductiveapertures 152 (conically shaped to receive the posts) in the gasketelement, withdraw from the apertures when the gasket is removed. Theconductive posts shown are simply the ends of wires, bent 90 degrees topoint upwardly, and stripped of insulation (the wider portion of theposts in the drawing is the wire with insulation; the narrower portionof the posts is the wire stripped of insulation). The conductiveapertures (into which the posts extend) can be made from plated brassalloy with multiple fingers to engage the posts.

A general block diagram of the defibrillator is shown in FIG. 20.Processing circuitry and associated software (processing 160) is at theheart of the defibrillator. Inputs from sensors 162 such as theaccelerometer in the CPR puck and the ECG monitoring electrodes on oneof the electrode assemblies are received through signal conditioning anddetection circuitry 164, 166. A user interface 168 provides outputs to adisplay 170 (and possibly to lights that direct the user to graphicalimages 172) and to an audio system 174 with speaker 176 and microphone178.

Many other implementations other than those described above are withinthe invention, which is defined by the following claims. As mentionedearlier, it is not possible to describe here all possibleimplementations of the invention, but a few possibilities not mentionedabove include the following: The condition sensor can also be used todetermine whether a liquid-containing element of other types of medicaldevices has dried out or lost sufficient liquid that is is not likely tobe suited to work properly. For example, the sensor could be provided inthe packaging for conductive pads used with defibrillation paddles, orwith moist pads used for ultrasonic imaging.

Not all of the features described above and appearing in some of theclaims below are necessary to practicing the invention. Only thefeatures recited in a particular claim are required for practicing theinvention described in that claim. Features have been intentionally leftout of claims in order to describe the invention at a breadth consistentwith the inventors' contribution.

What is claimed is:
 1. A defibrillator and associated electrode packagecontaining at least one defibrillation electrode for providing adefibrillation pulse to electrodes applied to the chest of a patient,the defibrillator and associated electrode package comprising a pair ofelectrical outputs at the defibrillator for delivering thedefibrillation pulse to the at least one defibrillation electrode,wherein the defibrillation electrode includes a metallic layer inelectrical contact with a conductive liquid-containing layer configuredfor delivering electrical current to a patient when the electrode hasbeen applied to a patient, the conductive liquid-containing layer beingsubject to drying out as liquid from the liquid-containing layervaporizes and travels from the interior space to the externalenvironment; an electrochemical cell separate from the defibrillationelectrode and formed within the package; a pair of electrical inputs atthe defibrillator for measuring the electrical potential of theelectrochemical cell formed within the package containing the at leastone defibrillation electrode prior to use of the electrode wherein theelectrochemical cell is separate from and composed of elements notshared with the conductive liquid-containing layer of the defibrillationelectrode; processing circuitry and associated software within thedefibrillator for comparing the electrical potential to one or morethresholds to determine whether a gel layer of the defibrillationelectrode remains sufficiently moist for the electrode to function; andconductors for connecting the pair of electrical outputs from thedefibrillator to the defibrillation electrode within the package and forconnecting the electrochemical cell within the package to the pair ofinputs at the defibrillator.
 2. The defibrillator and associatedelectrode package of claim 1 wherein the comparison determines whetherthe electrical potential is below a threshold.
 3. The defibrillator andassociated electrode package of claim 2 wherein the comparisondetermines whether the rate of change of the electrical potential isabove a threshold.
 4. The defibrillator and associated electrode packageof claim 1 wherein the processing circuitry and associated softwareincludes the capability to call for delivery of a warning indication tothe user based on the outcome of the comparison.
 5. The defibrillatorand associated electrode package of claim 1 wherein at least onethreshold is determined by reading a value stored in a memory deviceassociated with the defibrillation electrode.